1. Field of the Invention
The present invention relates to an insulation displacement terminal fitting and to a method for producing an insulation displacement terminal fitting.
2. Field of the Invention
Some insulation displacement terminal fittings are produced by applying plating to a surface of a planar conductive metal plate of a specified thickness. The metal plate then is stamped to specified shape. The stamping is carried out to define two U-shaped slits in portions of the metal plate that will define side walls of the terminal fitting. The cut portions surrounded by the U-shaped slits then are bent away from the plane of the plate to define blades, and the portions of the plate that will define the side walls are bent toward one another and into substantially parallel relationship. Thus, inwardly facing edges of the blades are substantially opposed to each other and act as cutting edges.
The opposed cutting edges of the blades are intended to contact the core of a wire that is urged into the space between the blades. These cutting edges are fractured surfaces formed at the time of stamping and are not protected by plating. Thus, there is a problem of contact reliability if these unplated surfaces are brought into contact with the core. Accordingly, plating generally has been applied to the fractured surfaces. Such plating at a later stage means an increased number of operation steps, which results in higher production costs.
In view of the above, insulation displacement terminal fittings that do not require plating at a later stage were developed. One example of such terminal fittings is disclosed in Japanese Unexamined Patent Publication No. 50(SHO)-114592. This terminal fitting is formed by striking the side walls with a press to form inwardly projecting V-shaped blade portions that project from the corresponding side wall of the terminal fitting. Each V-shaped blade portion has a pair of substantially triangular blades that meet at a fold line. The fold line between the blades serves as a contacting edge. Each blade also has an upwardly facing cutting edge. A wire can be pushed between an opposed pair of such V-shaped blade portions. As a result, the cutting edges of the blades cut a resin coating of the wire to expose the core. The contacting edge of each blade portion then contacts the exposed core. The folded contacting edges of the V-shaped blade portions remain plated, and thus plating at a later stage is unnecessary.
Blades formed by cutting and bending portions of the side walls are L-shaped when viewed in a direction in which the wire is pushed in. Thus, resistance created during insulation displacement is relatively small because the planar blades contact the resin coating of the wire while the wire is being pushed in. However, the blade portions formed by embossing are V-shaped when viewed in the direction in which the wire is pushed in. Accordingly, an insulation displacement resistance is disadvantageously large.
In view of the above, an object of the present invention is to provide an insulation displacement terminal fitting and a production method to reduce an insulation displacement resistance of V-shaped blade portions.
The subject invention is directed to an insulation displacement terminal fitting with at least one pair of blade portions. The blade portions area arranged such that a wire can be pushed between the blade portions in the pair at an angle different from 0xc2x0 and 180xc2x0 to the longitudinal axis of the wire, and preferably substantially normal to the longitudinal axis of the wire. Each blade portion comprises two blades that meet at a contacting edge. Each blade has a cutting edge that faces in a wire pushing direction and that extends from the contacting end of the blade portion. An insulation coating of a wire pushed between the two blade portions in a pair can be cut by cutting edges of the blades so that the core of the wire can be brought into contact with the contacting edges. The cutting edges of the two blades are arranged to contact the insulation coating at different times as the wire is pushed between the blade portions in the pair.
According to a preferred embodiment, the insulation displacement terminal fitting comprises side walls, and the blade portions are formed by bending or embossing portions of side walls inwardly. The blade portions preferably project substantially in a V-shape when viewed in a pushing or insertion direction of the wire.
Most preferably, the contacting edges extend continuously in the wire pushing direction from the end of the blades most distant from the respective side wall.
The two blades of the V-shaped blade portion are configured to avoid simultaneously coming into contact with the resin coating as the resin is being cut. Rather, one blade of a blade portion contacts and cuts the insulation coating before the other blade of the blade portion. Thus, resistance during cutting can be small.
The cutting edges of the two blades in each blade portion preferably form a substantially V-shape and are inclined from a corresponding side wall of the insulation displacement terminal fitting toward the corresponding contacting edge. The inclination is aligned in a direction to guide the wire laterally, and the contact timings of the cutting edges of the two blades in the blade portion with the insulation coating are determined by the angles of inclination of the cutting edges. The inclination of the cutting edges of the blades enables the position of the wire to be corrected even if the wire is displaced with respect to its widthwise direction.
The position or height of the blades along the wire pushing direction can be changed to vary the timing of the contact between the insulation coating and the cutting edges of the blades.
Each blade portion in the pair is configured to bring one blade into contact with the resin coating before the other blade in the respective blade portion. Thus, an insulation displacement resistance is smaller as compared to a case where such a sequential cutting operation is performed only at one of the blade portions in the pair.
One of the cutting edges in one blade portion may be parallel to a cutting edge in an opposed blade portion when viewed in the wire pushing direction. In this embodiment, the parallel cutting edges may contact the resin coating at the same time.
If the front cutting edge of the left blade portion and the front cutting edge of the right blade portion first come into contact with the wire, then the wire is pressed in oblique directions by the respective cutting edges due to an elastic restoring force of the resin coating while the resin coating is being cut. Thus the wire is pushed along the longitudinal direction of the wire by additional pushing forces from the two cutting edges that act in directions oblique to the longitudinal axis. More particularly a force acting in an obliquely forward direction to the right is given from the front cutting edge of the left blade portion and a force acting in an obliquely forward direction to the left is given from the front cutting edge of the right blade portion.
However, in the preferred embodiment, the cutting edge on the first blade portion that initially contacts the wire and the cutting edge of the second blade portion that initially contacts the wire are parallel to each other when viewed in the wire pushing direction. Thus, these two cutting edges effectively function as a single blade. As a result, the wire pushing forces from the cutting edges cancel each other, and there is no chance of displacing the wire along the longitudinal direction.
The invention also is directed to a method for producing an insulation displacement terminal fitting. The method comprises forming slits at locations on a flat metal piece that will define folds between the side walls and the bottom wall. The method proceeds by setting three transversely extending folds in an area where each slit is formed, and embossing portions of the side walls for forming the blade portions. Portions of the metal piece that will define the side walls then are folded toward one another.
According to a preferred embodiment of the invention, substantially triangular notches are formed in portions of the plate piece that correspond to upper ends of the side walls after bending and where the blade portions are to be formed. Two inclined edges of each of the substantially triangular notches correspond to the cutting edges of the blades.
These and other objects, features and advantages of the present invention will become apparent upon reading of the following detailed description of preferred embodiments and accompanying drawings.